What if I replace volt switch with charge beam and give him choice specs? id there a reason to pick one over the other?

That won't really work, because that would be assuming Jolteon would be staying in for a while locked into one attack, and with the fact that ground types, and things that resist electric aren't that uncommon, you're better off going with volt switch. With volt switch at least you can try to get some damage down on the opponent and switch out to safety, kinda giving you the advantage with the boost from specs (and you can switch with ground types appearing anyway), while with just charge beam you're relying on the special attack boosts that don't happen 100% of the time and yeah being locked into that is not useful. It can work with LO (but without volt switch as PlatDude said), since you can use different attacks, but not specs. :x

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